This invention relates to a method of synchronously driving a photosensitive member and a copy web in a copying apparatus and an apparatus suitable for carrying such method into practice.
When color duplication of an original in color is carried out by using an electrophotographic copying apparatus of the type in which each of toner images formed on a photosensitive member, by the steps of charging, exposing and developing, is transferred to a copy web, a plurality of toner images of different colors obtained by separating the color of the original, are successively transferred to the copy web to produce a copy of the original in color. In this case, the color of the copy obtained would not match the color of the original if the toner images of different colors were not in register with one another when they are superposed and transferred to the copy sheet. The toner images of different colors are often brought out of register with one another when the movement of the photosensitive member and the movement of the copy web are not in synchronism with one another.
When both the photosensitive member and the copy web are driven to move through a transmission system including gears and chains, the positions in which the gears and chains are brought into meshing engagement with one another would vary, when the pitch of the gears and chains is changed, thereby causing a change in the printing pressure applied to the copy web and the photosensitive member when printing is carried out. Irregularities in backlash caused by a jitter phenomenon or discrepancy in velocity caused by irregularities in the pitch of the gears and chains would render color registry impossible and cause distortion of the printed image or errors in the size of the duplicates to be produced. These phenomenons would have influences on the quality of the copy in color obtained by copying.
When a belt formed of rubber and pulleys are used for driving a photosensitive member and copy web, synchronism is not achieved due to slip of the belt.